This invention generally relates to apparatus and methods for analyzing a biological material to ascertain whether a particular substance is present or absent. More particularly, this invention relates to such apparatus and methods wherein the biological material is preferably human blood serum and the substance whose presence or absence is to be determined is preferably a composition indicative of disease, commonly referred to as an antigen. For example, in one aspect of this invention, human blood serum is analyzed to determine whether a hepatitis B surface antigen is present or absent.
Apparatus and methods for analyzing blood serum to ascertain whether a disease is present are especially important in situations where blood is donated by members of the public for the purpose of being subsequently administered to others by transfusion. In such cases it is necessary to analyze the donated blood to ensure that it is free from disease, lest the future user unknowingly contract that disease as a result of such transfusion. The disease for which analysis is most frequently conducted is hepatitis, though other diseases, including AIDS, may also be the subject of such analysis. Thus, though the descriptions referred to herein may specifically refer to hepatitis, it should be understood that such disease is exemplary rather than limitative, the scope of the invention being defined by the appended claims.
In one desirable apparatus for analyzing blood serum for substances indicative of disease, a rotatable incubation wheel is provided for moving a multiplicity of blood serum-containing cartridges to a plurality of operating stations. Such cartridges typically include a plunger, longitudinally movable through a cylindrical cavity containing the blood sample to be analyzed. A polystyrene bead, coated with a disease specific antibody or antigen, is ordinarily placed inside the cylindrical cavity of the cartridge, where it can be contacted by a quantity of blood serum subsequently placed therein. As explained hereinafter, as the multiplicity of cartridges are moved by the incubation wheel through the various operating stations, various substances are introduced into the cartridge cavity where they are brought into contact with the antibody-coated or antigen-coated polystyrene bead. Depending on the nature of the substances so introduced, and whether the blood serum contains a substance characteristic of the disease that is the object of the analysis then being undertaken, the contents of the cavity may be assayed to provide a "positive" or "negative" indication of that disease.
Though blood analyzing apparatus and methods of the type described have been successfully employed, they are not without certain drawbacks and deficiencies. Accordingly, it is a primary object of this invention to provide improved apparatus and methods useful in conjunction with apparatus for determining whether a particular quantity of blood serum is characterized by a substance indicative of a particular disease. It is another object of the invention to accomplish the foregoing, at least in part, by providing an air/liquid sensing device which helps ensure that liquid necessary for conducting the analysis has indeed been passed from a liquid reservoir to the cartridge containing the coated bead. It is yet another object of this invention to provide such a air/liquid sensing device which accomplishes these results in a reliable, hands-free operation.